1. Field of the Invention
The present invention relates to a single-detent binder for holding loose-leaf paper sheets, and in particular, a single-detent binder that is provided with a pull rod and locking pieces so as to enhance the locking function.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
In order to insert or take out loose-leaf paper sheets conveniently, a single-detent binder (also known as a loose-leaf ring binder) is widely used for a file folder or a note book. As known in the prior art, a typical single-detent binder mainly comprises an elongate curved housing, a pair of elongate baseplates, a plurality of ring shaped components and one or more control handles. The two longitudinal sides of the housing are bent inwards to form two inner sides. The pair of baseplates is located inside the cavity formed by the curved housing, so that one of the two longitudinal sides of each baseplate abuts upon the inner side of the housing while the longitudinal sides on the other side of the baseplates are interconnected in parallel, thus forming a central hinge possessing a pivot axis. Each baseplate is fixedly connected to a plurality of half ring shaped elements. At least one end of the loose-leaf binder is usually connected to a control handle, and the control handle is able to operate one pair of baseplates and move the central hinge upwards or downwards, so that the half ring shaped elements connected to the baseplates reciprocate between the open and closed positions.
A typical loose-leaf ring binder has a defect that the when the half ring shaped elements close, they cannot occlude together reliably. If the mechanism falls accidentally, the ring shaped components may be opened unexpectedly. As is known in the prior art, a single-detent binder can also comprise a locking system, thus enhancing the locking function and preventing the ring shaped components from being opened unexpectedly. The locking system usually comprises a pull rod and a plurality of locking components. The pull rod is positioned between the housing and baseplates, and the locking components are positioned on the locking portion of the pull rod and protruded towards the direction of the baseplates. The locking components are able to reciprocate together with the pull rod between the locking position at which the pivoting movement of the baseplates is blocked and the unlocking position.
The prior single-detent binder possessing a locking system is of relatively complex design. Firstly, each locking component demands a specific shape that matches the openings on the baseplates. Secondly, the pull rod is positioned between the housing and baseplates, and the housing demands a specific shape and thickness for accommodating the pull rod and the protruding locking components on its surface. Thirdly, the initial force of the typical single-detent binder comes from the force applied to the control handle, but the applied force cannot be evenly transferred to the whole baseplates under certain circumstances (for example, the housing is slightly deformed), thus causing a failure in pivoting of the baseplates.